Material testing machine including a control system for feedback-controlling the operation of a servo system

A material testing machine for measuring a mechanical property of a test piece based on a load given to the test piece and a mechanical change generated in the test piece, while feedback-controlling an operation of a servo system, including a hydraulic actuator which gives the load to the test piece, by means of a controller, such that actual load applied to the test piece coincides with target load, comprising:

• load controls means for periodically changing a target load in the feedback control to thereby periodically change a load given to the test piece;
• error detection means for determining at least one of an amplitude and an average value of a controlled variable in the feedback control, for every target load changing cycle, based on a peak value and a bottom value of the controlled variable which changes with a change in the load, and for determining at least one of first and second errors based on at least one of the amplitude and the average value of the controlled variable and at least one of an amplitude and an average value of the target load, the first error being an error between the amplitude of the controlled variable and the amplitude of the target load, the second error being an error between the average value of the controlled variable and the average value of the target load;
• correction means for correcting at least one of the amplitude and the average value of the target load in accordance with at least one of the first and second errors determined by said error detection means;
• a waveform generator for generating a testing waveform which indicates a target load in the feedback control,
• wherein said waveform generator includes:
• a waveform data memory storing therein a series of basic signal values which are sampled from a basic waveform so as to pick up a characteristic of the basic waveform;
• waveform data reading means for reading out the series of basic signal values from said waveform data memory and for repetitively reading out at least one basic signal value a repetitive number of times which is determined by a thinning number, to thereby obtain temporary signal values;
• thinning compensation means for correcting, in accordance with the thinning number, those temporary signal values which do not correspond to any of sampling points at which the basic signal values are sampled from the basic waveform, to thereby obtain a temporary testing waveform which is similar in shape to the basic waveform;
• and
• testing waveform generator means for adjusting an amplitude of the temporary testing waveform to thereby obtain a testing waveform.